Diapsids

The subclass Diapsida is one of the three
major amniote reptile lineages (along with Anapsida and Synapsida).
It is one of the most diverse vertebrate groups. First seen in the
Late Carboniferous (c. 315 mya), it includes all living reptiles except turtles,
in other words, lizards, snakes and crocodiles, as well as the birds, and many extinct
groups including dinosaurs, pterosaurs and ichthyosaurs.
Each of the six major subgroups - the Lepidosauria, Euryapsida,
Ichthyosauria, Crocodylomorpha, Dinosauria and Class Aves - has
its own site which describes it in more detail. These can be found
on the Chordata
homepage.